The present invention, generally, relates to electrical capacitor structures and, more particularly, to a new and improved structural arrangement for a capacitor which admits of functioning in a wider temperature range than prior structures.
In the past, no single capacitor could be used in an environment that involved wide temperature variations. It is known that changes in operating temperature can produce changes in the value of a capacitor.
Also, there is a continuing effort in the data processing field to develop equipment having less cost, greater operating speed and smaller size. The need for smaller sizes of capacitors produces a nagging problem in the microelectronics area today, because there are so many capacitors needed, and the problem arises due to the need to use two capacitors in order to cover the wider ranges of environmental temperatures to which computer systems are exposed today.
In today's systems, a single capacitor that is required for operation in an environment that involves a temperature range, from the higher temperature of today's data processing circuits down to the much colder cryogenic circuits, can fall short in its operation. Usually, a single capacitor in this environment will be replaced with two capacitors, producing an undesirable duplication in that more space is required for two capacitors.
Modern ferroelectric chip capacitors have made it possible to produce capacitor values ranging from a few picofarads to a few microfarads requiring much less spacial size than is possible using non-ferroelectric material. However, it has been found that the dielectric constant of such ferroelectric capacitors changes appreciably in response to changes in ambient temperature.
Microelectronic components used in high frequency operating circuit environments, particularly used in the switching of integrated circuits, can produce transient energy being coupled into other, unwanted circuit areas. This can be avoided by using a decoupling capacitor across the current source. Even the beneficial effects of a decoupling capacitor connected in this circuit can be affected adversely when temperature variations produce changes in the value of the capacitor.
An example of an early attempt at developing a decoupling capacitor with a better stability in a high frequency noise environment is the multilayer construction described in U.S. Pat. No. 4,667,267 to Hernandez et al. While the structure described in that patent may be effective to accomplish the purpose intended, it states that the decoupling capacitor of that structural arrangement is affected adversely and the value of the capacitor becomes unstable as temperature changes.
In U.S. Pat. No. 4,706,162, Hernandez et al. describes different constructions for a multilayer capacitor in order to overcome difficulties with inductance and to fit within a small space in an integrated circuit. Here, again, it is admitted that capacitance values change as temperature changes, and the decoupling capacitor is affected adversely, becoming unstable, as temperature changes.
U.S. Pat. No. 4,831,494 to Arnold et al., which is assigned to the same Assignee as the present invention, describes a multilayer capacitor structure that reduces the internal inductance even further, is smaller in size and is adapted to easier manufacturing techniques. However, it is not concerned with capacitor functioning effectively over a wide range of operating temperatures.